1. Field of the Invention
The present invention relates generally to a remote control system of serial-to-parallel (serial/parallel) conversion type. More particularly, the invention is concerned with an improvement of a remote control system of serial/conversion type which comprises a central control station and at least one local station located remotely from the central control station and connected thereto, wherein control pulse signals are serially sent from the central control station to the local station through the medium of a power transmission line, the local station being so implemented as to control in parallel a plurality of devices connected in response to reception of the control signals.
2. Description of the Prior Art
In the field of the automatic control technology, such a remote control system is well known and widely employed in which a multiplicity of devices, instruments or equipment such as, for example, solenoid valves or the like are controlled by control signals sent from a control station installed remotely from these objectives to be controlled.
In the remote control systems of the type mentioned above, there arise a lot of such applications where the device to be controlled are miniaturized and, provided in a great number, being arrayed densely to one another, as a result of which a great difficulty is encountered in making access to the individual devices. Consequently, provision of individual control signal lines, clock signal lines, power supply lines and others between the control station and the devices to be controlled involves much labor, large space and high costs. Besides, maintenance is attended with very troublesome procedure.
As the typical examples of the device to be controlled, there may be mentioned an automated tool such as, for example, an industrial robot which is designed to be hydraulically controlled with the aid of electromagnetic valves also referred to as the solenoid valve. In most of such automated tools or robots, a so-called manifold solenoid valve unit incorporating integrally a number of solenoid valves is used for controlling hydraulically various parts of the tool with a view to reducing the space occupied by the valves. However, in order to remotely control the individual solenoid valves realized in the form of the manifold valve unit from a control station, a number of lines inclusive of the control signal lines, the power supply line and others have to be installed between the control station and the individual solenoid valves, respectively, which of course involves high expenditure as well as a large space.
As an attempt for mitigating the difficulty mentioned above, there has already been developed a remote control system in which at least a local station is provided in association with the central control station, wherein the devices to be controlled are connected to the outputs of the local station. For controlling the devices, serial control signals are sent from the central control station to the local station where the serial signals are converted to parallel signals for controlling the devices connected to the outputs of the local station. With this arrangement, it is only necessary to interconnect the central control station and the local station. In other words, direct interconnection of the individual devices to be controlled and the central control station is rendered unnecessary. As a result, the number of the lines required for transmission of the control signals, electric power and others can be correspondingly decreased.
An example of the control system mentioned just above is disclosed in Japanese Patent Application Laid-Open No. 88081/1986 (JP-A-61-88081). For having a better understanding of the invention, this prior art control system will be described below by reference to FIGS. 6a and 6b of the accompanying drawings, in which FIG. 6a is a block diagram showing an arrangement of the prior art control system and FIG. 6b is a timing chart for illustrating operation of the same.
In FIG. 6a, a reference numeral 60 denotes a control circuit serving as a central station, and numerals 61 and 62 denote conversion circuits, respectively, which are adapted to generate signals for controlling solenoids SOL1 and SOL2, and SOL3 and SOL4 of solenoid valves (not shown) on the basis of signals sent from the control circuit or central control stations. Further, reference numerals 611 and 621 denote shift registers, respectively, each of which comprises two stages of flip-flops, and finally reference symbols RA1 to RA4 denote latch circuits for holding signals for driving the solenoids SOL1, SOL2, SOL3 and SOL4, respectively. Needless to say, each of the conversion circuits 61 serves as a local station.
Now, operation of the system shown in FIG. 6a will be described by reference to the timing chart shown in FIG. 6b. A data line 600, a clock line 601, a latch line 602 and, power lines 603-605 of the ground level, 5 V and 24 V, respectively, are provided for connecting each of the conversion circuits (local stations) 61 and 62 and the control circuit (central control station) 60 to each other. A data signal (control signal) capable to assuming logic "1" level (for energization of solenoid or ON control) or logic "0" level (for deenergization of solenoid or OFF control) is sent out onto the data line 600 in synchronism with the clock pulses generated at time points t1-t4 shown at the first row in FIG. 6b. In the case of the illustrated example, the data signal consists of a pulse sequence of "1", "0", "1" and "1" in this order.
Assuming now that the logic "1" pulse signal is applied to a shift terminal SI of the shift register 611 constituting a part of the conversion circuit (local station) 61 at the time point t1 from the central control station 10 via the data line 600 in synchronism with the clock signal inputted to the clock terminal CK of the shift register 611 via the clock line 601, then the pulse signal of logic "1" is outputted from an output terminal Q1 of the flip-flop constituting the first stage of the shift register 611 to be applied to a data input terminal of the latch circuit RA1. At that time, it is assumed that no latch signal is supplied via the latch line 602. Consequently, the output signal from the terminal Q1 is not latched by the latch circuit RA1.
Upon application of the data signal of logic "0" to the input terminal SI of the shift register 611 at the time point t2, the output from the first stage of the shift register 611 is then logic "0", while the second stage thereof outputs logic "1" at an output terminal Q2 in response to the shift of logic "1" from the first stage. At the time point t3, the data signal of logic "1" is applied to the terminal SI of the shift register, while the output of logic "1" from the output terminal Q2 of the second stage of the shift register 611 is applied to the shift input terminal SI of the shift register 621 of the conversion circuit 62 via connection DO-DI.
In this manner, there make appearance the data signals of logic "1", "1", "0" and "1", respectively, at the output terminals Q1 and Q2 of both the shift registers 611 and 621 at the time point t4, as can be seen in FIG. 6b. In succession, the latch signal is produced by the central control station 60 and applied to the input terminals D of the latch circuits RA1, RA2, RA3 and RA4, whereby the logic outputs "1", "1", "0" and "1" from the output terminal Q1 and Q2 of the shift registers 611 and 621 are latched and held by the latch circuits RA1, RA2, RA3 and RA4, respectively. In response to the outputs Q of these latch circuits, switches (not shown) provided in association with the outputs of the latch circuits are correspondingly operated, whereby the solenoids SOL1, SOL2 and SOL4 are electrically energized by electrically power supplied from the central control station 60 via the power supply line 605, while the solenoid SOL3 remains deenergized because the associated switch is not actuated due to the output of logic "0" at the output terminal Q of the latch circuit RA3. Needless to say, the energization of the solenoids SOL1, SOL2 and SOL4 results in actuation of the associated electromagnetic valves. Parenthetically, the power transmission line 605 serves for supplying power for operating the solenoids, while the power line 604 serves to supply power for energizing the conversion circuits 61.
As will be appreciated from the foregoing, the prior art remote control system shown in FIG. 6a requires as many as six lines in total for the transmission of the command signal, control signals and power from the central control station to the local stations, involving no little expensiveness.